Since its introduction, the gene targeting technique has led to a number of mile-stone observations in mammalian biology. By selectively disrupting a gene of interest, it offers the potential to precisely define the function of a particular substance. The Applicant enlists this technology to evaluate his long-standing interest in the role of the renin- angiotensin system (RAS) in renal modeling (normal development) and remodeling (disease). Encouraged immensely by recent success in producing deletion mutant mouse strains in three key angiotensin-related genes and by several strikingly abnormal phenotypes demonstrated within their kidneys, the Applicant now aspires to identify the mechanisms underlying these phenotypes which implicate heretofore unrecognized important biological function of angiotensin. Reaching this goal appears challenging: The precise site and nature of abnormal phenotype resulting from gene targeting must be defined within the organ made up of highly heterogeneous cell populations, with each cell type having distinctive - and important - homeostatic functions. Additionally, the phenotype specific to the removal of local action of angiotensin must be isolated amongst the systemic circulatory, metabolic and humoral influences of angiotensin. The Applicant trusts that the modern technology will, once again, offer effective tools to reach his goal by overcoming these obstacles. The proposed project has two intended goals, namely, to refine the gene targeting methodology for cardio-reno-vascular research and, by employing the latter, to define the role of angiotensin in renal modeling and remodeling. Once these goals are achieved, both methodology and recombinant animal models are expected to become new effective tools for other investigators to enter a new stage of their investigation.